1. FIELD OF THE INVENTION
The present invention relates to a crank in which a crank arm is engaged with a crank pin by press fitting.
2. DESCRIPTION OF THE RELATED ART
It is known that a crank for use with an internal combustion engine is produced by engaging a crank pin with a crank arm by press fitting. In this case, in order to compensate for the joining force required to join the crank pin and the crank arm together, a thin film such as a copper plating is formed over each of the press-fitting surfaces of the crank pin and the crank arm which are brought into contact with each other when they are engaged by press fitting. Thus, the clearance between the press-fitting surfaces is filled with such a thin film to enhance the coefficient of friction therebetween and increase the tightness of press-fitting of the crank pin with respect to the crank arm, thereby increasing twist torque.
However, such a related art method involves the following problems. Although the twist torque can be increased by increasing the tightness of press-fitting, a certain limitation is imposed on the related art method since there is a risk of involving a excessive deformation or the breakage of members. Also, it has been necessary to work each member with an extremely high precision.